Measured-value sensors for magnetic-inductive flowmeters

Abstract

A measured-value sensor for an inductive flowmeter comprises a fluid impermeable sintered ceramic measuring tube adapted to be positioned in a conductive-liquid flow path. Magnetic coils surround the tube and are adapted to apply a magnetic field to a conductive liquid traversing the path. A pair of diametrically opposite measuring electrodes contact the liquid traversing the path for tapping an induced voltage across the electrodes representing the flow of the liquid along the path, each of the electrodes having a metallic shaft traversing the tube substantially radially and sealingly sintered to the material of the tube. The ends of the ceramic measuring tube are provided with a flange, ground at its peripheral wall surface and fastened by shrinkage stress in a bore of a steel casing. After sintering of measuring tube, conductive paths are manufactured for the formation of grounding rings and other current-conducting components by applying a platinum paste on the ceramic measuring tube and reheating again subsequently. In the process, the paste compacts to form a thin conductor film which is firmly anchored on the surface of said measuring tube.

We claim: 
     
       1. In a measured-value sensor for a magnetic-inductive flowmeter, comprising an electrically insulating ceramic measuring tube which is arranged inside a steel housing and provided on two opposite sides with measuring electrodes which pass radially through the wall of the measuring tube and with magnet coils arranged on the wall, the improvement wherein said measuring tube is composed of a tight burnt ceramic material into which shafts of the measuring electrodes are sintered in a leakproof manner. 
     
     
       2. A measured-value sensor in accordance with claim 1 wherein the measuring tube consists of a ceramic material selected from the group which consists of oxide ceramics, carbides, nitrides, borides, steatites and aluminum-magnesium-silicates. 
     
     
       3. A measured-value sensor in accordance with claim 1 wherein each sintered-in shaft is shaped in the form of a solid pin or a tube with a plate which lies in a recess formed along the inside of said wall of the measuring tube. 
     
     
       4. A measured-value sensor in accordance with claim 1 wherein each sintered-in shaft has the shape of a tube with a plate which forms the electrode surface. 
     
     
       5. A measured-value sensor in accordance with claim 1 wherein each sintered-in shaft has the shape of a little tube into which is inserted from the inside of the measuring tube a pin that is sealed-welded to the rim of the little tube located outside of the measuring tube. 
     
     
       6. A measured-value sensor in accordance with claim 1 wherein the measuring tube is fastened with its ends through shrinkage stress in bores of said steel housing. 
     
     
       7. A measured-value sensor in accordance with claim 6 wherein a bearing ring of ceramic or metallic material is fastened through shrinkage stress at each end of the measuring tube and that the measuring tube with the aid of these bearing rings is fastened through shrinkage stress in respective bores of said steel housing. 
     
     
       8. A measured-value sensor in accordance with claim 1 wherein the measuring tube is provided at its ends with flanges turned radially to the outside and that with the aid of these flanges the measuring tube is fastened through shrinkage stress in respective bores of said steel housing. 
     
     
       9. A measured-value sensor in accordance with claim 8 wherein the peripheral wall surfaces of the flanges are ground to an outer diameter that permits a shrink fit in the bores of said steel housing. 
     
     
       10. A measured-value sensor in accordance with claim 1 wherein said measuring tube has flanges with peripheral wall surfaces which are sealed by gluing or cementing in respective bores of said steel housing. 
     
     
       11. A measured-value sensor according to claim 1 wherein a conductive path forming a grounding ring is conductively connected to a least one face of the measuring tube with a grounding connection. 
     
     
       12. A measured-value sensor in accordance with claim 11 wherein the conductive path forming the grounding ring is applied onto a chamfer which enlarges the inner surface of the wall of the measuring tube and the conductive path is connected to one or more conductive paths serving as grounding connections disposed radially at the face of said measuring tube. 
     
     
       13. A measured-value sensor in accordance with claim 1 wherein a conductive path is applied to the outer surface of the wall of said measuring tube, the conductive path being conductively connected with the shaft of one measuring electrode and extending to about one half of the circumference of the connector point for a conducting wire to a single converter. 
     
     
       14. A measured-value sensor for an inductive flowmeter which comprises: a thread-spool-shaped fluid impermeable tight-burned ceramic measuring tube composed of a material selected from the group which consists of oxide ceramics, carbides, nitrides, borides, steatite and aluminum-magnesium silicates and adapted to be positioned in a conductive-liquid flow path, said measuring tube comprising a cylindrical wall having annular flanges at opposite ends thereof, the peripheries of said flanges being ground;   a steel casing receiving said tube, said casing surrounding said wall and having a pair of axially spaced bores, said peripheries of said flanges being respectively received with sealingly tight shrink fits in said bores;   a magnetic coil within said casing, surrounding said wall and adapted to apply a magnetic field to a conductive liquid traversing said path; and   a pair of diametrically opposite electrodes contacting the liquid traversing said path for tapping an induced voltage across said electrodes representing the flow of liquid along said path, each of said electrodes having a metallic shaft traversing said wall substantially radially and sintered therein in a leakproof manner.   
     
     
       15. The sensor defined in claim 14, further comprising a conductive strip burned on an end face of said tube formed by one of said flanges for grounding. 
     
     
       16. The sensor defined in claim 15 wherein said strip is formed on an outwardly divergent surface defined by a chamfer at said end face.